Triggering device for spark generators



April 23, 1968 s. BARBINI TRIGGERING DEVICE FOR SPARK GENERATORS FiledMarch 8, 1966 3 Sheets-Sheet 1 v ZNVENTOR SPARTACUS BARBINI .A T RNEYApril 23, 1968 s. BARBINI 3,379,928

TRIGGERING DEVICE FOR SPARK GENERATORS Filed March 8, 1966 5Sheets-Sheet 2 FIG. 4 34 FIG. 5

FIG. 6

SPARTAC US BARBINI April 23, 1968 s. BARBINI 3,379,928

TRIGGERING DEVICE FOR SPARK GENERATORS Filed March 8, 1966 5Sheets-Sheet 8 FIG.7

FIG.8

14 QOOOOOOl IS QOQOOOOOOOO INVENTOR SPARTHCUS B RBINI United StatesPatent 3,379,928 TRlGGEs NG DEVIQE FOR SPARK GENERATORS SpartacusBarhini, Chenille, France, assignor to Compagnie Generale dElectricite,Paris, France, a corporation of France Filed Mar. 8, 1966, Ser. No.532,680 Claims priority, application France, Mar. 12, 1965,

a 10 Claims. ci. sis-s7 This invention relates to spark generatorsincluding an electric circuit having at least two electrodes and astorage device for electrical energy such as a condenser. Moreparticularly, the invention concerns a novel device for triggering aspark between the electrodes upon the generation in the circuit of ahigh intensity electric current.

it is known to use triggering devices for high power spark generatorscomprising an auxiliary or triggering electrode disposed in the gap andconnected to a voltage source which is capable of delivering an impulseof sufficiently large amplitude for ionizing the relatively narrow spaceseparating the auxiliary electrode from one of the principal electrodes.Such devices sometimes give rise to dificulties in that the triggeringelectrode may deflect a part of the principal discharge; such anoccurrence is totally contrary to the intended results. On the otherhand, the known structures of triggering electrodes and the energysupply device connected therewith may cause problems of insulation dueto the large potential differences between the triggering electrode onone hand and the parts of the spark generator on the other hand duringtriggering and discharge.

The object of the invention is, therefore, to eliminate thedisadvantages inherent in spark generators used heretofore whereinauxiliary trig ering electrodes are provided in addition to theprincipal electrodes.

Another object of the invention is to provide an improved triggeringdevice having a simplified structure that disposes of the necessity ofusing heavy electrical insulatron.

Still another object of the invention is to provide an improvedtriggering device that does not need expensive and complicated auxiliaryapparatus.

Other objects and advantages of the invention will be better understoodfrom the ensuing specification taken in conjunction with the drawing,wherein:

FIG. 1 is a basic diagram of a spark generator according to theinvention;

FIGS. 2, 3, 4 and 5 show four embodiments of a triggering electrodeaccording to the invention;

FIGS. 6 and 7 show modifications of the generator shown in FIG. 1; and

FIG. 8 shows a spark generator particularly adapted for use with theelectrode depicted in FIG. 5.

The generator shown in FIG. 1 comprises a condenser 1 connected by meansof conductor 2 to an electrode 3 which, together with electrode 4, formsthe spark gap per se. Electrode 4 is grounded across a load 5 having arelatively small internal resistance. The spark gap constituted byelectrodes 3 and 4 may be surrounded by ambient atmosphere or may beplaced in an enclosure formed, for example, by tube 8 which may betransparent and closed at its extremities by means of two terminal walls99. The structure of electrodes 3 and 4 will become apparent later inconnection with the description of FIG. 2, 3, 4 and 5. The enclosuresurrounding the electrodes 3 and 4 may be filled with air or gas of highor low pressu e depending upon the requirements regarding thecharacteristics of the spark.

The apparatus further comprises an electric coil 10 for generating amagnetic field parallel to the axis 3,379,928 Patented Apr. 23, 1968defined by electrodes 3 and 4. The conductor 6 of the coil 10 isconnected to a voltage source 7. This voltage source supplies impulsesof very short duration and of relatively high power when energized by anappropriate control device (not shown).

Turning now to FIG. 2, there is shown a first embodiment of an electrodeaccording to the invention. This electrode comprises a generallyelongated cylindrical stem 22 having an extended part 21 surrounded by aconductor 24 having a helical shape of varying radius. One end 26 ofhelix 24 is afiixed -to the stem 22, while the other end 25 is free andis disposed at a short distance from the reduced tip or end portion 23of extension 21. The helix 24 may comprise either a tubular or a solidconductor and may have a cross-section of any desired configuration.Helix 24 is preferably inscribable in a spherical or ellipsoidalsurface. The stem 22 may be filled with a material 28 having goodmagnetic characteristics such as ferrite or an agglomerated iron powderbase. Since stem 22 is placed Within the magnetic field generated bycoil 10, the magnetic filling 28 serves to concentrate the magneticfield thus improving the operation of the novel triggering device. Stem222 is provided with an elongated slot 27 for interrupting the loopformed by the metallic tube and thus preventing the generation ofFoucault currents.

The apparatus schematically shown in FIG. 1 and having an electrode 3 ofthe type shown in FIG. 2 operates in the following manner:

The coil 10 functions as the primary coil of a transformer, thesecondary coil of which is constituted by the helicoidal conductor 24.When a voltage impulse is applied to coil 19, a very high voltage isinduced in the helicoidal conductor. This voltage produces a sparkbetween the extremities 23 and 25, ionizing the gas sur rounding thespark gap triggering the discharge of condenser 1 across the gap.

One of the principal advantages of the novel triggering device is thatthe electrode maintains throughout a generally coaxial structure. Thehelix 24 functions both as an auxiliary triggering electrode and as aprincipal discharge electrode since the extremities 23 and 25 are bothat the same potential at the moment when the main spark is triggered inthe generator. Thus, this device is clearly distinguishable from knowngenerators having an auxiliary electrode that is separated andelectrically insulated from the principal electrodes. Such auxiliaryelectrodes may, on the one hand, easily be damaged by the principaldischarge of the generator and, on the other hand, may arrest one partof the electric are thus lowering the current passing through load 5.

In the embodiment shown in FIG. 1, the coil 10 constituting the primarycoil of the transformer is disposed coaxially with and externally of theelectrode assembly.

In the modification shown in FIG. 6 the coil 11 is disposed about theelectrode carrying the helicoidal conductor 24.

FIG. 7 shows still a further modification of the generator schematicallyshown in FIG. 1. According to FIG. 7 the coil 12 functioning as theprimary coil of the transrormer is made of a spiral lying in a singleplane and embedded in an insulating material of any desired type thatalso has good mechanical qualities. The flat disc thus obtained mayserve as one of the terminal walls of the enclosure surrounding theelectrodes constituting the spark gap.

FIG. 3 shows a modification of the embodiment illustrated in FIG. 2. Asseen in FIG. 3, the part 21 is embedded in a mass 29 of insulating andheat-resistaing material. This material may preferably consist offiberglass contained in a synthetic heat hardening material. The mass 29preferably has a spherical or ovoidal surface of revolution providedwith a groove 30 of substantially helicoidal shape. In this groove thereis disposed an electric conductor 24, one end 26 of which is afiixed totube 22, while the other end 25 functions as a triggering electrodedisposed adjacent the extremity 23 of part 21. The conductor 24- ispreferably made of a copper or bronze band, while the part 21 of theprincipal electrode may be made entirely or partially of tungsten ortungsten alloy.

FIG. 4 illustrates another embodiment of the novel electrode. Theelectrode shown in FIG. 4 comprises a cylindrical part 32 similar tostem 22 of FIGS. 2 and 3, an extension 31 forming the principalelectrode and a conductor 34 of a spiral configuration lyingapproximately in a plane perpendicular to members 3132. The end of theexternal turn of spiral 34 is aflixed by means of a metallic member 36to the cylindrical part 32, while the end of the turn having thesmallest diameter is free and carries a reduced terminus or end portion35 disposed at a relatively short distance from the end 33 of part 31.

The electrode shown in FIG. 5 is a modification or" that illustrated inFIG. 4. According to the embodiment shown in FIG. 5, the supporting stemis solid and may have any cross-sectional configuration. The spiral isreduced to a single turn 37 having a shape constituting a ring orincomplete annulus and is provided with a gap 38, the edges of whichconstitute a small auxiliary triggering spark gap. The edge 39 of turn37 forms the surface where the principal electric spark will begenerated.

FIG. 8 schematically shows a generator particularly adapted toelectrodes shown in FIG. 5. There is shown a coil 16 embedded in thecylinder 13 forming the lateral wall of the enclosure containingelectrodes 14 and 15 that are preferably of the same type. The coil 16surrounds both electrodes so as to increase the magnetic field to thegreatest extent possible and thus compensate for the decrease of themagnetic coupling due to the single spiral of coil 16.

The advantage of the apparatus shown in FIG. 8 resides in that theelectric impulse sent through coil 16 will induce the current in theloops of the two electrodes 14 and 15 and will thus increase theefficiency of the triggering of the principal spark.

Although several embodiments of the invention have been depicted anddescribed, it will be apparent that these embodiments are illustrativein nature and that a number of modifications in the apparatus andvariations in its end use may be effected without departing from thespirit or scope of the invention as defined in the appended claims.

That which is claimed is:

1. In a spark generator of the type including two electrodes providedwith free ends to define a spark gap, the improvement comprisingtriggering means integral with at least one of said electrodes, saidtriggering means including an auxiliary spark gap defined by the endportions of two spaced and electrically interconnected conducting partsof said electrode, at least one of said parts forming at least part of aloop, means for generating a magnetic field adapted to pass through saidloop for inducing an electromotive force therein to generate an ionizingspark in said auxiliary gap for triggering a spark between said freeends of said electrodes.

2. The improvement as defined in claim 1, wherein said one electrodeincludes a generally cylindrical metallic tube filled with aferromagnetic material adapted to concentrate said magnetic field, oneof said parts extending from one end of said tube along the axisthereof.

3. The improvement as defined in clairn 1, wherein one of said parts isan elongated, substantially straight member, the end portion of whichconstitutes said free end, the other of said parts is a helix having aplurality of turns and being disposed coaxially about said member.

4. The improvement as defined in claim 3, wherein said helix isinscribable in at least a portion of a substantially ovoidal surface.

5. The improvement as defined in claim 4, wherein said helix surroundsan electrically insulating and heatresisting ovoidal body provided witha bore through which said straight member extends.

6. The improvement as defined in claim 5, wherein said helix isdeposited as a metal layer or band on the surface of said body.

7. The improvement as defined in claim 1, wherein one of said parts isan elongated, substantially straight member, the end portion of whichconstitutes said free end, the other of said parts is a spiral coaxialwith said member and lying in a plane substantially normal thereto.

8. The improvement as defined in claim 1, wherein said parts form asingle ring interrupted by said auxiliary gap, one peripheral edge ofsaid ring constituting said free end.

9. The improvement as defined in claim 1 including an elongatedenclosure surrounding said electrodes, said means for generating amagnetic field comprises at least one flat coil embedded in athermosetting material and forming at least one end cap for said,enclosure, one of said parts being an elongated, substantially straightmember disposed coaxially with respect to said coil.

10. The improvement as defined in claim 1 including a cylindricalenclosure surrounding said electrodes, said means for generating amagnetic field comprises a helically wound coil disposed about at leastone of said electrodes and embedded in said enclosure.

No references cited.

JAMES W. LAWRENCE, Primary Examiner.

P. C. DEMEO, Assistant Examiner.

1. IN A SPARK GENERATOR OF THE TYPE INCLUDING TWO ELECTRODES PROVIDEDWITH FREE ENDS TO DEFINE A SPARK GAP, THE IMPROVEMENT COMPRISINGTRIGGERING MEANS INTEGRAL WITH AT LEAST ONE OF SAID ELECTRODES, SAIDTRIGGERING MEANS INCLUDING AN AUXILIARY SPARK GAP DEFINED BY THE ENDPORTIONS OF TWO SPACED AND ELECTRICALLY INTERCONNECTED CONDUCTING PARTSOF SAID ELECTRODE, AT LEAST ONE OF SAID PARTS FORMING AT LEAST PART OF ALOOP, MEANS FOR GENERATING A MAGNETIC FIELD ADAPTED TO PASS THROUGH SAIDLOOP FOR INDUCING AN ELECTROMOTIVE FORCE THEREIN TO GENERATE AN IONIZINGSPARK IN SAID AUXILIARY GAP FOR TRIGGERING A SPARK BETWEEN SAID FREEENDS OF SAID ELECTRODES.